This invention relates to a device for feeding documents and more particularly to an improved vacuum cup feeder mechanism used in such a device.
The invention described below is particularly well suited and designed for use in document handling apparatuses such as mail handling and processing equipment. For example, as illustrated in U.S. Ser. No. 148,068 filed on May 12, 1980 entitled "Vacuum Document Feeder" there is illustrated an envelope feeding device which withdraws envelopes from a stack and places them into a main document transport or feeder which is comprised of a belt or drive roller system. The envelopes are weighed and sorted in the main document transport. The envelopes are pulled from the stack by means of a vacuum cup which is oscillated or reciprocated back and forth between the stack and the main document transport. The vacuum cup is designed to remove one envelope at a time and deliver that envelope to the transport system, typically with a speed and/or change of direction in the envelope.
Another example of a main transport system which can use the disclosed inventive device includes inserters which withdraw inserts from a stack by means of gripper jaws and places them on a raceway as illustrated in U.S. Pat. No. 3,306,606. Yet another type of main transport system is represented by automatic mail sorting machines wherein address envelopes are optically read and sorted according to zip code destinations. A characteristic of all of these drive systems is a positive, hard drive of the document to assure accurate positioning of the document into the transport system. Another characteristic is that it must be fully automatic and operate at high speeds to be economically efficient.
One problem with the prior art devices using vacuum cups occurs at the interface between the vacuum cup feeder and the main transport. As the vacuum cup must be able to separate a single envelope or document from a stack, the vacuum cup is generally made of soft accommodating material. This enables the vacuum cup to firmly seat against the document regardless of slight irregularities in the document or its misregistration as the vacuum cup mechanism can be moved quickly and positively against the document. After the document is withdrawn from the stack, it is placed into the main transport system. The vacuum must be released at precisely the instant that the document is fed into the main transport system to prevent damage to the vacuum cup as the document is pulled off of the cup and to prevent damage or excessive wear to the main transport system.
Typically, prior art devices have used a solenoid actuated vacuum valve coupled with a position sensor to release the vacuum to the vacuum cup at the proper instant in the document feeding cycle. Other similar devices have used cams and cam sensors to control the valve timing. Because the vacuum valve must be located remote from the vacuum cup due to its size and operation, a significant time delay occurs before the vacuum at the vacuum cup is reduced through the length of connecting tubing. With a variable speed feeder the higher the feed rate, the longer the time delay will be with respect to the feed cycle. At extremely high feed rates it is very difficult to time the valve and have the vacuum reduced at the cup quickly enough to allow the document to be easily pulled off the vaccum cup. If the vacuum is not sufficiently reduced there will still be a sufficient vacuum present to damage the cup and thereby reduce its useful life.
One solution has been to employ a registration surface to register the material stack for proper timing into the main transport. However, a problem with this is that misregistration will also cause the vacuum to be released at other than the optimum desired times. Also, for systems using pull out or nip rollers, material of greater thickness will be picked up by the rollers before the thinner material, causing further timing changes.
In order to compensate for all of the timing variables when feeding varying thicknesses and types of documents at varying speeds, prior devices had to compromise the feeder design in order to minimize wear. Furthermore, the use of solenoid valves and position sensors resulted in higher system costs and less reliable feeding.